In the manufacture of lineal members, it is well known to use an electrostatic spray painting process to paint the members. The lineal members can be pultruded members or other types of elongated work pieces. For example, the lineal members could be wood molding strips which are sprayed with a varnish solution in a continuous process. Other lineal members have a plastic surface. Examples of these are pultruded members, extruded members, and other inline molded lineal members. An example of these is a lineal used in a fiberglass window frame, i.e., a lineal comprised of a glass wool core and a hard resinous outer coat.
Electrostatically painting these inherently nonconductive surfaces creates some problems. One of the solutions to enable an electrostatic painting process to be successful on a non-conductive product is to bury a conductive wire or web beneath the surface of the lineal member. The conductive material could then be grounded to provide an electrically attractive force for the charged paint particles in an electrostatic painting process. Another solution to the problem is to coat the lineal with a conductive solution, particularly a salt solution, which, when evaporated, will leave salt ions on the surface of the lineal. The salt ions remaining on the surface provide a sufficient conductive layer in order to act as a ground, thereby attracting the charged spray painted particles.
It has been found that when a plastic surface is to be spray painted, the use of a solvent as the carrier for the salts to be applied to the surface is very advantageous. The solvent evaporates quickly, and enables the conductive solution to disperse and spread uniformly on the surface of the lineal, thereby evenly distributing the salt ions on the lineal surface.
Unfortunately, the use of a solvent based conductive solution in preparation for an electrostatic painting process has some drawbacks. The solvents are potentially hazardous materials, and their use results in health and safety issues, and hazardous waste disposal penalties. Attempts to replace the solvent based conductive solutions with aqueous conductive solutions have not been successful. Aqueous solutions do not disperse as uniformly as solvent based solutions on the surface of plastic lineals. Also aqueous systems do not dry as readily as the solvent based conductive solutions.
It would be useful to have a non solvent-based carrier for the conductive solution, while still maintaining the solvent advantages of dispersibility on the lineal surface and quick evaporation of the carrier medium.